Blowing nozzle for a highly pressurized gaseous fluid

ABSTRACT

A blowing nozzle for a highly pressurized gaseous fluid comprising at least two narrow slot-form exhaust passages (12) having a width (d) insignificantly larger than the size of polluting particles occurring in said fluid and a length (L) no more than ten times the average width (d) of each slot, the exhaust passages extending in parallel or radially over the end surface of the nozzle in a projection perpendicular to its longitudinal axis.

CROSS REFERENCE TO RELATED APPLICATION(S)

This United States application stems from PCT International ApplicationNo. PCT/SE86/00263 filed June 5, 1986.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention concerns a blowing nozzle for a highly pressurizedgaseous fluid comprising at least two narrow exhaust passages having awidth insignificantly larger than the size of particles, occurring insaid fluid.

Description of the Prior Art

Blowing nozzles are used for various industrial purposes, e.g. to blowaway cuttings from a boring and other debris from a workpiece, to coolduring welding or other kind of heat generating work, as exhausts frompneumatic machines, or for drying of paint.

A major problem with these devices is the risk of the noise levelbecoming hazardous, when a high blowing power is needed. Noise levelsaround 113 dB (A) are not uncommon for blowing nozzles with high output.

Noise reducing blowing nozzles are known, e.g. from Swedish patentapplication No. SE 7806883-0, which has several small circular passages.These small passages must be drilled with a very high degree ofprecision, in order to achieve the desired noise reducing effect.Because of the necessity for a high degree of precision these nozzlesare comparatively expensive to manufacture. At the same time the blowingforce possible with one of these nozzles is limited, which means thatseveral nozzles must be mounted in parallel in order to reach a desiredlarge blowing force. This means that these noise-reducing blowingnozzles in many cases are a very expensive solution to the noiseproblem.

BRIEF SUMMARY OF THE INVENTION

The object of the present invention is therefore to produce a cheap andefficient nozzle with noise reducing properties, and by which it ispossible to reach a considerably larger blowing force for a givenfrontal area, compared with corresponding known blowing nozzles.

The invention is characterized in that the exhaust passages areslot-formed, each having a length, no more than ten times the averagewidth of each slot, and that they extend in parallel or radially overthe end surface of the nozzle, in a projection perpendicular to itslongitudinal axis.

According to one advantageous embodiment of the invention, the depth oraxial length of each slot-formed exhaust passage is at last five to tentimes the length of said slot.

Preferably several exhaust passages are formed in parallel with thelongitudinal axis of the nozzle in a central body, which is surroundedby a casing.

According to another advantageous embodiment of the invention the nozzlehas a circular front with exhaust passages radially arrangedconcentrically around a common longitudinal axis, wherein theslot-formed exhaust passages are arranged with a minimum individualdistance (distance between centers) of three times the slot width.

Preferably, the passages, as seen along their longitudinal axis, divergeradially outwardly with respect to the surrounding casing. Preferably,the central body protrudes from the casing in order to increasecoejection of atmospheric air surrounding the nozzle.

A nozzle having a rectangular front and parallel exhaust passagespreferably has a distance between passages that is at least three timesthe square root of the product of slot length multiplied by the slotwidth.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in the following in greater detailwith reference to the accompanying drawings, wherein:

FIG. 1 is an end view of a circular nozzle according to a firstembodiment of the invention;

FIGS. 2a and 2b are cross-sectional views taken along line II--II inFIG. 1 showing two different embodiments of the invention;

FIG. 3 is an end view of a second embodiment of a circular nozzle of theinvention;

FIG. 4 is an end view of a rectangular nozzle according to theinvention;

FIG. 5 is a cross-sectional view taken along line V--V in FIG. 4;

FIG. 6 is a cross-sectional view taken along line VI--VI in FIG. 7;

FIG. 7 is a side elevational view of another embodiment of theinvention, shown in 5:1 scale; and

FIG. 8 is a cross-sectional view taken along line VIII--VIII in FIG. 7.

DETAILED DESCRIPTION

The nozzles of this invention comprise a central body 10 withlongitudinal parallel slots and is surrounded by a thin wall casing 11.The slots form narrow exhaust passages 12 together with the casing 11,wherein the passages have a cross-sectional length L no more than tentimes the cross-sectional width d of the slots and a depth, or axiallength, t at least five to ten times the length of the slots.

When a gas is evacuated to the atmosphere from a closed system at highspeed through a passage or conduit a turbulence is created, whichgenerates a very loud noise. Since it is easier to dampen highfrequences of sound, it is acoustically advantageous to replace a largepassage by several small passages. The maximum generation of sound for acircular passage takes place at a frequency f_(max) which isproportional to diameter d of the passage and therefore the diametershould be selected as small as possible.

For a rectangular passage according to the invention, the f_(max) hasproven to be proportional to the square root of the product of slotlength L multiplied by the slot width d, up to very high factors of L/d.It will, however, not be practical to use larger values for L/d than 10.(Note that f_(max) will only be proportional to d for values of L/d≈100and higher, but this is of no concern in the field of blowing nozzles.)Preferably the maximum frequency should be close to or even above 15,000Hz, i.e. above the normal upper limit for human hearing. For this reasonthe exhaust passages 12 are as narrow as possible, without risk forclogging by debris in the exhaust air. At the same time sufficientoutlet area is achieved by the number of exhaust passages, which numbercan be varied depending on the needs.

A risk while using several adjacent exhaust passages, is that they mayfunction acoustically like one large opening, lif they are relativelysituated too close. For this reason the distance between the slot-formedexhaust passages are about three times the width d of one slot, and theydo not extend further than about half the outer radius R_(y) towards thecenter of the nozzle.

It has also been found that the generation of noise is reduced when anair jet can convey the surrounding gas. To enable this the nozzleexhaust passages should be placed near the outskirts of the nozzlefront. This conveying of surrounding gas can be enhanced when thecentral body 10 protrudes axially out of the casing.

From FIGS. 2a and 2b it appears that the slot-formed exhaust passages 12reach far into the nozzle. Experiments have proven that the generationof noise is gradually reduced by increasing slot depth t, until the slotdepth reaches a value between five to ten times the slot length L. Thesmaller value relates to a diverging passage, i.e. as in the embodimentof FIG. 2b.

FIG. 3 shows a variant of the nozzle according to the invention, whereinthe slots have two different lengths L₁ and L₂ respectively. Thisembodiment enables a larger blowing capacity for a given frontal area.This arrangement, however, results in a slightly higher sound level.

FIGS. 4 and 5 show a rectangular nozzle according to the inventionhaving four exhaust passages 12 extending through a central body 10,which is surrounded by a four-sided casing 11. As in the above describedcircular nozzle, the exhaust passages are narrow and slot-formed. Thedistance between the passages are at least three times the square rootof the product of slot length L multiplied by the slot width d. Theexhaust passages 12 can be cut into the central body from both the longsides, so that the body is maintained in one piece, which can be pushedaxially into the casing 11. Just as in the former embodiment, the slotlength L is no more than ten times the slot width d and the slot depth tis at least five to ten times the slot length L. The passages can alsobe made converging in the direction of the gas stream towards the nozzlefront.

FIGS. 6, 7 and 8 show a variant of the invention wherein the exhaustopening 12, as seen in their radial cross-section, diverge radiallyoutwardly. This embodiment is especially preferable when producing verynarrow blowing nozzles having a frontal diameter of about 5 mm. In thisembodiment the exhaust passages can extend radially further in towardsthe center of the nozzle since they diverge as mentioned above, withoutconflicting with the condition that the smallest distance betweenadjacent passages must be three times the width of the slot-formedpassages, which contributes to a further increased blowing force for anygiven nozzle frontal area. If the nozzle is pointed as shown in FIGS. 7and 8 its accessibility is enhanced and it can be used to clean verysmall drill holes.

Tests made with the nozzles according to the invention to compare themwith a conventional blowing nozzle having circular passages with thesame total outlet area (80 mm²) and the same working pressure (600 kPa)and the same blowing force (20 N at a distance of 10 cm) haveestablished that the noise is reduced from 113 dB(A) for theconventional nozzle, to 96 dB(A) for the new nozzle. This very largereduction of noise will significantly reduce the cost when building newfactories or can be utilized to improve conditions within existingfactories.

One reason for the surprisingly good test results for the nozzleaccording to the invention is its ability to convey surrounding air.

Traditionally the inner form of a exhaust passage has been considered tohave no importance for the generation of noise which takes place withinthe turbulence outside the nozzle. However, an air jet leaving a hole ina thin wall can cause a back flow along the fringes of the hole, whichback flow increases the turbulence and the generation of noise.

The proportionally large depth of the slot-formed passages at thenozzles according to the invention prevents this back flow and thereforecontributes to the lowered noise level.

The invention is not limited to the above described embodiments andseveral variants are possible within the scope of the accompanyingclaims. The central body can be molded, cut or extruded at acomparatively low cost.

I claim:
 1. A blowing nozzle for a highly pressurized gaseous fluidcomprising:at least two narrow exhaust passages each in the form of aslot having a closed, substantially rectangular cross-section having alongitudinal axis, a cross-sectional width insignificantly larger thanthe size of particles occurring in said fluid, a cross-sectional lengthof no more than ten times the average width of each slot, and a depth inthe direction of said longitudinal axis of at least five to ten timessaid length of said slot; said longitudinal axes being substantiallyparallel.
 2. A blowing nozzle as claimed in claim 1 wherein:said nozzlehas a central longitudinal axis and comprises a central body and acasing surrounding said central body in contacting engagement therewith;and said at least two passages comprise several exhaust passages in saidcentral body extending parallel to said longitudinal axis of the nozzle.3. A blowing nozzle as claimed in claim 1 wherein:said nozzle has acentral longitudinal axis and a circular cross-sectional shape; and saidexhaust passages are arranged in circular spaced relationship about saidcentral longitudinal axis with the cross-sectional lengths of said slotsextending radially, the spacing between the centers of adjacent slotsbeing a minimal distance of three times said cross-sectional width.
 4. Ablowing nozzle as claimed in claim 2 wherein:said nozzle has a circularcross-sectional shape; and said exhaust passages are arranged incircular spaced relationship about said central longitudinal axis withthe cross-sectional lengths of said slots extending radially, thespacing between the centers of adjacent slots being a minimal distanceof three times said cross-sectional width.
 5. A blowing nozzle asclaimed in claim 3 wherein:said passages diverge radially outwardlyalong said longitudinal axis of said passages in the direction of thenozzle outlet.
 6. A blowing nozzle as claimed in claim 4 wherein:saidpassages diverge radially outwardly along said longitudinal axis of saidpassages in the direction of the nozzle outlet.
 7. A blowing nozzle asclaimed in claim 5 wherein:each slot has radially inner and outersidewalls; and said inner sidewall diverges radially outwardly from aposition adjacent said central longitudinal axis of said nozzle towardthe nozzle outlet.
 8. A blowing nozzle as claimed in claim 4wherein:said central body protrudes from said casing at the nozzleoutlet so that conveyance of atmospheric air surrounding the nozzle isincreased.
 9. A blowing nozzle as claimed in claim 6 wherein:saidcentral body protrudes from said casing at the nozzle outlet so thatconveyance of atmospheric air surrounding the nozzle is increased.
 10. Ablowing nozzle as claimed in claim 8 wherein:said protruding centralbody comprises a protruding part having a conical surface providing asubstantially pointed outlet end for the nozzle.
 11. A blowing nozzle asclaimed in claim 1 wherein:said nozzle has a rectangular cross-sectionalshape; said slots are parallel; and the distance between adjacent slotsis at least three times the square root of the product of said slotlength multiplied by said slot width.
 12. A blowing nozzle as claimed inclaim 3 wherein:said slots diverge radially outwardly in radialcross-section.
 13. A blowing nozzle as claimed in claim 4 wherein:saidslots diverge radially outwardly in radial cross-section.
 14. A blowingnozzle as claimed in claim 8 wherein:said slots diverge radiallyoutwardly in radial cross-section.
 15. A blowing nozzle as claimed inclaim 10 wherein:said slots diverge radially outwardly in radialcross-section.